1. Field of the Invention
The present invention relates generally to semiconductor packages, and more particularly, to a stack package made of a plurality of area array type chip scale packages.
2. Description of the Prior Art
The miniaturization of semiconductor packages has progressed very rapidly during the past ten years in order to keep up with the miniaturization of electronic devices. This progression of miniaturization has been especially prevalent in the field of mobile electronic devices because of the wide spread usage of chip scale packages (CSP). However, chip scale packages have a disadvantage when compared with conventional lead frame type packages because of the difficulty in using them with package stacking technology.
Stack packages, which are made by stacking a plurality of packages, have been developed and widely used to increase the installation density of chips. The stack package is different from a multi chip package (MCP), which is made by installing a plurality of chips in a package. The multi chip package has advantages in package size and package installation convenience. However, productivity of the multi chip package can be low because often chips that have not been tested for their quality are used, and if even one of the installed chips is inferior in performance, the entire multi chip package becomes inferior. On the contrary, the productivity of the stack package is usually superior to that of the multi chip package because all of the packages used for the stack package are tested. Therefore, even though both methods are available, the stack package is the preferred method to enhance chip installation density because of its reliability.
Chip scale packages are generally area array type packages, which are more inappropriate for stacking than lead frame type packages. There has been much effort to develop chip scale packages suitable for package stacking. Three examples of chip scale packages suitable for the stack package are disclosed in FIG. 1-FIG. 3.
FIG. 1 shows a well-known conventional type stack package 600 made of a plurality of chip scale packages. Each stacked chip scale package is a fan-out type ball grid array package 610. As shown in FIG. 1, a semiconductor chip 611 is installed and electrically connected to a beam lead 622 on a circuit board 620. A plurality of solder balls 637 are positioned on the peripheral area of the circuit board 620 and are connected to the semiconductor chip 611 through the beam lead 622.
One problem with the chip scale package 610 disclosed in FIG. 1, is that it is difficult to standardize the arrangement of the solder balls 637, because the arrangement of the solder balls 637 must be designed according to the size of the installed chip. For example, a 512 Mb DRAM chip cannot be installed in a package designed for a 256 Mb DRAM chip. This severely limits the versatility of this type of chip scale package stack.
FIG. 2 shows another conventional type stack package 700. Referring to FIG. 2, each stacked chip scale package 710 is made by attaching a chip 711 to a carrier tape 720 by beam lead bonding. The outer leads 737 of the stacked chip scale packages 710 are electrically connected to each other. In this kind of stack package, it is difficult to standardize each stacked package because the length of the outer leads 737 of each stacked package varies according to the stacked level. This non-standardization of lead parts results in production cost increases.
FIG. 3 shows a further conventional type stack package 800. Referring to FIG. 3, the stack package 800 comprises a plurality of fan-out type chip scale packages 810 and a conventional ball grid array (BGA) type chip scale package 805. The BGA type chip scale package 805 is stacked at the lowest level. The solder balls 837 are formed on the entire area of the BGA type chip scale package, and function as Input/Output ports of the stack package 800. This kind of stack package has the same technical drawback, i.e. the difficulty of standardizing the solder ball arrangement, as that of the stack package 600.